Hammer control circuit in a high speed printer



Get. 12, 19% T. SAPINO ETAL 3,211,087

HAMMER CONTROL CIRCUIT IN A HIGH SPEED PRINTER Filed Nov. 28, 1961 fir. g' +33 #24 T. no 182 Fig. 2

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Solenoid Pulse Streicher HOLD INFORMATION r: STROBE INVENTORS THEODORE SAP/NO ALAN J. DEERFIELD BY ga am ATTORNEY United States Patent 3,211,087 HAMMER CONTROL CIRCUIT IN A HIGH SPEED PRINTER Theodore Sapino, Framingham, and Alan J. Deerfield,

Franklin, Mass., assignors to Honeywell Inc., a corporation of Delaware Filed Nov. 28, 1961, Ser. No. 155,343 9 Claims. (Cl. 101-93) The present invention relates in general to new and improved control apparatus, in particular to apparatus for providing a desired output response during an accurately controlled time interval.

Although the present invention is pertinent to a wide range of applications, it will be explained and illustrated with respect to a hammer driver control circuit for use with a high-speed printer which is employed as an output device of a computing system. Such an arrangement is described and illustrated in a copending application of Charles J. Barbagallo and Richard D. Pasciuto, Serial Number 113,351, filed May 29, 1961. The printer disclosed in that application contains print hammers which are selectively actuated to print chosen data characters on a paper medium that is positioned between the hammers and the raised characters of a rotating print roll. The control circuit must be capable of selectively energizing the print hammers for a percisely determined time interval. Any variation of the duration of the hammer energization may change the hammer travel time from the hammer rest position to the point of impact. Where this occurs, characters printed by the affected hammers will be displaced vertically with respect to the horizontal print line. Moreover, since the definition of the printed character is to some extent a function of the number of copies printed, such variations of the hammer travel time will further affect the clarity of the printed output.

In a printer of the type set forth in the above-mentioned copending application, the paper web is stationary pending the completion of printing of each line. During this period, the print roll executes one complete, revolution to present successive rows of raised characters to the print hammers, the latter being actuated in accordance with the data received from the computer to print the desired characters on the intermediately positioned Web. The speed of the operation is such, that the energization periods of the hammers actually overlap when successively presented characters are printed. Thus, it

is important that the initiation as well as the termination.

of the hammer energization periods be precisely determined.

In the past, one-shot multivibrators were employed to achieve such timing, the RC time constant of the multivibrator determining the duration of the energizing signal. high-speed printers, the signal timing of the energization must be accurate to within 1%. One-shot rnultivibrators, unless adapted at prohibitive cost to achieve such accuracy, are generally inadequate for this purpose.

Frequently, proper hammer timing is obtainable by adjusting each hammer actuating mechanism against the energizing signal received from the associated hammer driver control circuit. Such an arrangement, however, is not conducive to the free interchangeability of the control circuits to operate with different hammers. Such a requirement arises where, as in the apparatus described in the above-mentioned copending application, the 120 drive control circuits may, depending on the printing arrangement, be plugged to operate with different ones of a bank of 160 hammers. Where one-shot multivibrators are employed and the absolute uniformity of all the hammer energizing signals cannot be guaranteed,

With the printing speeds obtainable in modern an idle period is required to adjust the operation of the hammers against their new energizing signals.

It is a primary object of the present invention to provide apparatus which is selectively capable of providing a desired output response during a precisely determined time interval.

It is another object of the present invention to provide a simple and inexpensive control circuit which is capable of supplying an output signal of accurately timed duration.

In the invention which forms the subject matter of this application, the apparatus for providing the desired output response throughout a predetermined time period is dependent on externally supplied signals which are selectively adapted to initiate the output response. Further signals, each adapted to terminate the aforesaid output response, are provided intermediate the aforesaid initiating signals. In addition, there are provided means for rendering ineffective one or more of the aforesaid terminating signals following a selected signal which initiated the output response. The aforesaid predetermined time period is defined by the interval elapsed between the selected initiating signal and the first effective terminating signal.

The various novel features which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its advantages and specific objects thereof, reference should be had to the following detailed description and the accompanying drawings in which:

FIGURE 1 illustrates a preferred embodiment of the invention; and

FIGURE 2 illustrates certain waveforms associated with the operation of the apparatus of FIGURE 1.

With reference now to the drawings, FIGURE 1 illustrates the invention with respect to a control circuit which is adapted to energize a single print hammer of the aforesaid high-speed printer with an accurately timed signal. An amplifier 10 is seen to have its input connected to a gate buffer structure. Each hammer is energized by a circuit identical to that shown. The latter consists of the gates 12, 14 and 16, each buffered to the amplifier 10. The output of the amplifier is connected to an inverter 18 whose output signal appears at a junction point 19. The latter is connected to an amplifier 20 whose output is coupled to a hammer solenoid 22 which activates the hammer mechanism upon being energized. The junction point 19 is further connected to one input leg 23 of the gate 14, as well as to a pulse stretcher 24. The pulse stretcher may comprise a capacitive element connected between the point 19 and one input leg 26 of the gate 12. The other input leg of the gate 12 is connected to a terminal 28 which has a gate enabling signal normally applied thereto. The other input leg of the gate 14 has a hold signal applied thereto. An informtaion signal is applied to an input leg of the gate 16, while a strobing signal is applied to the other" input leg of the latter gate.

As previously explained, the above-mentioned highspeed printer comprises a print roll positioned opposite a bank of printer hammers. The print roll has successive rows of raised print characters, each row containing for example, identical characters. In accordance with the data received from the computer, the print hammers are selectively energized to strike the chosen characters of the print roll as the latter rotate into printing position and to effect a corresponding imprint on the intermediately positioned paper web. Inasmuch as the respective hammers are aligned in a row, the selection of a particular hammer will determine the particular column of the print line in which the chosen data character is to be imprinted. On the other hand, since the print roll completes a revolution to present all the data characters to the print hammer before the paper is moved to the subsequent printing line, the initiation of the energization of the selected hammer determines which data character is to be printed in the selected column. The duration of the hammer energization determines the speed of hammer travel toward its impact point and thus, within limits, determines the vertical position of the printed data character with respect to the print line.

Strobing pulses are applied to each control circuit in a fixed time interval prior to the appearance of the corresponding character row of the print roll in the printing position. In the case of the circuit shown in FIGURE 1, the strobing pulses enable the gate 16. The latter provides an output pulse so that the associated hammer may be selected by means of an information signal applied to the other leg of the gate 16. In the present example, it is assumed that the character rows on the print roll for the character A, B, C, D, etc. appear successively in printing position. The strobing pulses which are illustrated in FIGURE 2A are labeled correspondingly and are seen to be initiated at the times t r 01 [D1,

FIGURE 2B illustrates the information pulse which selects the hammer that is energized from the control circuit of FIGURE 1. In the illustrated example, the information pulse is applied to select the hammer for the printing of the character A and is seen to extend from t to t its duration is such that it overlaps the interval during which the strobing pulse for the character A is applied.

FIGURE 20 illustrates the holding signal which is applied to one input leg of the gate 14 as well as to corresponding gates in all other hammer drivers control circuits. The holding signal comprises a normally negative voltage level which is periodically interrupted by disabling or terminating pulses such as are initiated at times I 2' r etc. Each of these terminating pulses is seen to occur a fixed time interval after the preceding strobing pulse of FIGURE 2A, the precise timing being determined by the desired duration of the signal which is applied to the hammer solenoid. Both the strobing pulses as well as the terminating pulses of the holding signal may be derived from the same source synchronized to the rotation of the print roll so that separate clock pulse sources are not required.

When the information pulse shown in FIGURE 2B is applied to one input leg of the gate 16 between the times r and t the application of a strobing pulse to the other input leg of the gate at time t renders the gate conductive and applies an input pulse to the amplifier 10. Inasmuch as a single amplifier stage produces logical inversion, the amplifier output signal is applied to the inverter 18, before being fed back to the input. The amplified and inverted output signal which appears at the junction point 19 is illustrated in FIG- URE 2E. It is a bilevel signal which is switched from its initial level to the other level at time t From FIGURE 2C it will be seen that during the time interval t t the level of the holding signal is negative to enable the gate 14. Inasmuch as the logical signal inversion occurring between the input and the output of amplifier 10 is balanced out by the action of the inverter 18, the output signal of the latter, when fed back to the other leg 23 of the gate 14, applies a regenerative signal to the input of the amplifier 10. The regenerative signal is elfective to maintain the level of the output signal that was initiated by the strobing pulse A as long as the level of the holding signal remains negative. The occurrence of a terminating pulse at time t would normally be etfective to cut off the gate 14 and to remove the negative input signal applied to the input of the amplifier 10.

The signal which appears at the point 19 is further applied to the input of the pulse stretcher 24, the output signal of the latter being coupled to the gate input leg 26 of the gate 12. This regeneratively applied signal is illustrated in FIGURE 2D. As previously mentioned, gate 12 is normally energized by means of an enabling signal applied to the terminal 28, so that the pulse stretcher output signals will be coupled through the gate '12 to the amplifier 10. The action of the pulse stretcher causes the trailing signal edge to occur at time I i.e. after the terminating pulse which was initiated at time t has subsided. Inasmuch as the signal from the pulse stretcher is regeneratively applied to the input of the amplifier 10 by way of the gate 12, the eifect of the terminating pulse at time t on the amplifier is neutralized. Specifically, even though the gate 14 is cut off for the duration of the terminating pulse, the action of the pulse stretcher is effective to provide a regenerative amplifier input signal which in turn will maintain the level of the output signal at the point 19 negative. The precise time at which the trailing edge of the regenerative feedback signal from the pulse stretcher occurs is immaterial, provided only that it occurs after the terminating pulse which is initiated at time t has subsided.

As explained above, the pulse stretcher 24 may consist of a circuit which essentially interposes a capacitive element in series in the feedback loop. Inasmuch as the amplifier output signal which appears at point 19 approaches a steady-state condition at the negative voltage level, the signal from the pulse stretcher which is applied to the gate 12 will become Zero. The precise time when this happens is immaterial provided only that it occurs after the terminating pulse which is initiated at time t has subsided. Following the end of the terminating pulse, the gate 14 is again enabled by the negative holding signal level. Thus the amplifier output signal at point 19 is again fed back regeneratively by way of the gate 14 and the output signal of the amplifier 10 is maintained. Upon the occurrence of the next terminating pulse at time r the gate 14 is disabled and the signal which is applied to the input of the amplifier 10 becomes zero. The operation set forth above provides the hammer energization signal for the letter A which is shown in FIGURE 2E. It will be seen that the output signal of the amplifier 10 reverts to its original level thereby terminating the energization of the hammer solenoid 22. Thus the duration of the amplifier output signal extends from r to 2 This time interval may be adjusted by suitably phasing the terminating pulses shown at FIGURE 20 with respect to the strobing pulses of FIGURE 2A.

In a line-by-line printer of the type described herein, each hammer is normally actuated only once during the printing of a line. As previously pointed out, the high speed of printing requires an overlap of the energization periods of difierent hammers in the event that they are to print successively occurring data characters. FIGURE 2F illustrates an information signal which may be applied to the control circuit of a different hammer during the same revolution of the print roll in order to print the immediately following character B. The information pulse is seen to occur between the time r and t so as to overlap the duration of the strobing pulse which is initiated at time t As in the case of FIGURE 1, the resultant amplifier output signal, which is illustrated in FIGURE 2H, is regeneratively applied to the input of the control circuit as well as to a pulse stretcher. The signal derived from the latter unit is illustrated in FIGURE 2G and ends at time I i.e., after the occurrence of the terminating pulse initiated at time I As a consequence, the amplifier output signal shown in FIGURE 2H does not revert to its initial level until the arrival of the next terminating pulse at time t A comparison of FIG- URES 2E and 2H will show that the energizing signals of the respective hammers overlap during the time interval extending from I to I I As previously explained, the duration of the hammer energizing signal may be varied by suitably changing the timing of the terminating pulses of FIGURE 2C with respect to the strobing pulses shown in FIGURE 2A. The limit of this variation is determined by the spacing of the strobing pulses. If it is desired to shorten the duration of the energizing signal to an interval less than that determined by the spacing of the strobing pulses, it is merely necessary to open the second feedback loop of the circuit shown in FIGURE 1 which contains the pulse stretcher. This is accomplished by removing the gate enabling signal normally applied to the input terminal 28 of the gate 12. In that case, the first terminating pulse following the strobing pulse will be effective to switch the energizing signal off.

More frequently, however, it may be desirable to extend the duration of the energizing signal shown in FIGURE 2E beyond the occurrence of the second terminating pulse occurring at time In the latter case, it is necessary to provide a pulse stretching action which will delay the trailing edge of the applied signal to a point beyond the duration of the last terminating pulse which is to be rendered ineffective. This situation is illustrated in FIG- URES 21 and 2] for the printing of the character A. The trailing edge of the waveform of FIGURE 21 is seen to occur at time r so as to neutralize the terminating pulse which is initiated at time i Accordingly, the subsequent terminating pulse which is initiated at time is the first one to be effective to switch the output signal to its initial level.

From the foregoing discussion it will be clear that an accurate control of the duration of the energizing pulse is obtained by means of the strobing and terminating pulses which are synchronized to the rotation of the print roll.

RC time constants are relied on for timing purposes only in the pulse stretcher 24 where the timing is not critical. As explained above the trailing edge of the output signal of the pulse stretcher may occur at any time between the terminating pulses which start at 1 and t respectively, without altering the operation. Thus, the timing of the hammer energization is accurately controlled with the present invention, which provides uniformity with respect to all the hammers and permits different hammers to operate with the same control circuit.

As previously explained, the present invention is not limited to printer control circuits but is applicable wherever the duration of a desired output response is controlled by predetermined initiating and terminating signals and Where means for rendering ineffective at least one of said terminating signals must be provided.

From the foregoing disclosure of the invention, it will be apparent that numerous modifications, changes and equivalents will now occur to those skilled in the art, all of which fall within the true spirit and scope contemplated by the invention.

What is claimed is:

1. A control circuit comprising signal amplifying means adapted to provide an output signal of predetermined duration, means for receiving a sequence of strobing pulses, means for receiving an information signal, means for applying an input signal to said amplifying means upon the joint occurrence of said information signal and one of said sequence of strobing pulses, means for deriving a holding signal, means for deriving a regenerative feedback signal from said output signal, means upon the joint occurrence of said holding signal and said derived regenerative feedback signal for applying another input signal to said amplifying means, said holding signal including a sequence of disabling pulses corresponding to said strobing pulses and respectively lagging the latter by a predetermined time interval, each of said disabling pulses 6 being adapted to interrupt the application of said other input signal, and means for extending the duration of said derived regenerative feedback signal beyond the termination of said predetermined time interval and for applying it to said amplifying means, said last-recited regenerative feedback signal being adapted to neutralize the effect upon said amplifying means of the disabling pulse immediately following the occurrence of said one strobing pulse.

2. Apparatus for use with a data output device of the type having a plurality of transducers selectively adapted to transfer chosen ones of a sequence of data characters to a storage medium, a control circuit corresponding to each of said transducers and including signal amplifying means adapted to provide an output signal for energizing its corresponding transducer, means for receiving strobing pulses each corresponding to one of said data characters, means for receiving information signals each adapted to select one of said amplifying means for transferring a chosen data character to said medium by means of its corresponding transducer, means for gating each of said information signals with a strobing pulse to the input of said selected amplifying means to initiate said output signal, means for deriving a regenerative feedback signal from said output signal, means for receiving a holding signal, means for gating said derived regenerative feed back signal with said holding signal and for applying it to the input of said selected amplifying means, said holding signal including pulses respectively adapted to terminate said output signal by disabling said last-recited gating means a predetermined time interval after the occurrence of each strobing pulse, means for extending the duration of said derived regenerative feedback signal beyond the end of said last-recited time interval and for applying it to the input of said amplifying means; whereby said output signal is rendered insensitive to the holding signal terminating pulse immediately following its initiating strobing pulse.

3. Control apparatus comprising a circuit having an input and an output, means for deriving a bilevel signal at said output means for deriving a first series of pulses each adapted to initiate one level of said output signal, means for applying said first pulse series to said input, means for regeneratively feeding back said output signal to said input to maintain said one signal level at said output, means for deriving a second series of pulses each adapted to switch said output signal to the other signal level by rendering said regenerative feedback signal ineffective, means for applying said second pulse series to said input, and means for applying said regenerative feedback signal to said input with its trailing edge delayed by an interval sufiicient to render ineffective at least one of said second series of pulses immediately following a first series pulse initiating said one signal level.

4. Control apparatus comprising a circuit having an input and an output, means for deriving a bilevel signal at said output, means for deriving first pulses adapted to initiate one level of said signal, means for applying said first pulses to said input, means for regeneratively feeding back said signal to said input to maintain said one signal level at said output, means for deriving second pulses adapted to switch said signal to the other signal level, means for applying said second pulses to said input and means for rendering ineffective at least one of said second pulses immediately following a first pulse initiating said one signal level.

5. Apparatus for selectively providing a desired output response during a predetermined time interval, said apparatus including a circuit having an input and an output and further comprising means for providing signals selectively adapted to initiate said output response, means for applying said initiating signals to said input, means for maintaining said output response, means for providing signals occurring in time between the occurrence of said initiating signals adapted to terminate said output response, means for applying said terminating signals to said input and means for rendering ineffective at least one of said terminating signals following a selected initiating signal; whereby said predetermined time interval is defined by the time elapsed between said selected initiating signal and the first effective terminating signal.

6. In a control circuit adapted to provide an output signal having first and second signal levels, means for applying an initiating pulse to the input of said circuit adapted to provide an output signal having said first signal level, means for regeneratively feeding back said last-recited output signal to said input to maintain said first signal level, means for applying terminating pulses to said input each adapted to switch said output signal to said second level by disabling said feedback signal, and means for operating on said output signal and regeneratively applying it to said input, said operating means being adapted to extend the duration of said output signal at least beyond the occurrence of the first terminating pulse following said initiating pulse to render said first terminating pulse ineffective.

7. Control apparatus comprising a circuit adapted to provide a bilevel signal at its output, means for applying a series of strobing pulses to the input of said circuit each adapted to initiate one level of said output signal, means responsive to said output signal for applying a regenerative feedback signal to the input of said circuit adapted to maintain said one signal level at said output, means for applying a series of disabling pulses to said input each adapted to switch said output signal to the other signal level by rendering said regenerative feedback signal ineffective, each of said disabling pulses occurring a predetermined time interval after a corresponding strobing pulse, means for extending the duration of said regenerative feedback signal for a period beyond the end of said predetermined time interval, and means for applying said extended regenerative feedback signal to the input of said circuit to render ineffective at least the first occurring disabling pulse following a strobing pulse which initiates said one signal level.

8. Apparatus for use with a data output device of the type having a plurality of transducers selectively adapted to receive output signals to effect the transfer of chosen ones of a sequence of data characters to a storage medium, comprising amplifying means corresponding to each of said transducers adapted to provide said output signals, means for providing strobing pulses at the input of each of said amplifying means to initiate the output signal thereof, said strobing pulses corresponding respectively to the data characters of said sequence, means for gating said strobing pulses with information signals applied to energize chosen ones of said amplifying means,

means for deriving a regenerative feedback signal from said output signal means for maintaining each of said output signals by applying said regenerative feedback signal to the input of said amplifying means, means for applying a disabling pulse to each of said amplifying means following each strobing pulse adapted to terminate the output signal thereof, and means responsive to said regenerative feedback signal to apply a further signal to the input of said amplifying means for rendering ineffective the first disabling pulse following the strobing signal which initiated said output signal.

9. In a circuit for controlling the actuation of a selected one of a plurality of print hammers in synchronism with the appearance in printing position of a chosen one of a sequence of data characters positioned on a rotating print roll, an amplifier adapted to provide an output signal of predetermined duration to energize said selected hammer, first, second and third gates buffered to the input of said amplifier, means for applying a strobing pulse corresponding to each of said data characters to one input of said first gate, means for applying an information signal corresponding to said chosen data character to another input of said first gate to initiate said amplifier output signal upon the occurrence of the subsequently occurring strobing pulse, means responsive to said amplifier output signal for applying a regenerative feedback signal to one input of said second gate, means for applying a holding signal to another input of said second gate including disabling pulses each occurring a predetermined time interval after a strobing pulse, said holding signal being adapted to maintain said amplifier output signal between the occurrence of said disabling pulses, means for extending the duration of said regenerative feedback signal beyond said predetermined time interval, means for applying an enabling signal to one input of said third gate, and means for applying said extended regenerative feedback signal to another input of said third gate; whereby said predetermined duration of said output signal is defined as the time interval between said subsequent strobing pulse and of the second disabling pulse occurring thereafter.

References Cited by the Examiner UNITED STATES PATENTS 2,783,456 2/57 Steagall 30788.5 X 2,892,936 6/59 Paivinen 32855 2,939,388 6/60 Frogatt 10193 3,021,486 2/62 Kortf et a1. 32858 3,046,485 7/62 Brown 32891 ROBERT E. PULFREY, Primary Examiner.

ROBERT A. LEIGHY, WILLIAM B. PENN, Examiners. 

8. APPARATUS FOR USE WITH A DATA OUTPUT DEVICE OF THE TYPE HAVING A PLURALITY OF TRANSDUCERS SELECTIVELY ADAPTED TO RECEIVE OUTPUT SIGNALS TO EFFECT THE TRANSFER OF CHOSEN ONES OF A SEQUENCE OF DATA CHARACTERS TO A STORAGE MEDIUM, COMPRISING AMPLIFYING MEANS CORRESPONDING TO EACH OF SAID TRANSDUCERS ADAPTED TO PROVIDE SAID OUTPUT SIGNALS, MEANS FOR PROVIDING STROBING PULSES AT THE INPUT OF EACH OF SAID AMPLIFYING MEANS TO INITIATE THE OUTPUT SIGNAL THEREOF, SAID STROBING PULSES CORRESPONDING RESPECTIVELY TO THE DATA CHARACTERS OF SAID SEQUENCE, MEANS FOR GATING SAID STROBING PULSES WITH INFORMATION SIGNALS APPLIED TO ENERGIZE CHOSEN ONES OF SAID AMPLIFYING MEANS, MEANS FOR DERIVING A REGENERATIVE FEEDBACK SIGNAL FROM SAID OUTPUT SIGNAL MEANS FOR MAINTAINING EACH OF SAID OUTPUT SIGNALS BY APPLYING SAID REGENERATIVE FEEDBACK SIGNAL TO THE INPUT OF SAID AMPLIFYING MEANS, MEANS FOR APPLYING A DISABLING PULSE TO EACH OF SAID AMPLIFYING MEANS FOLLOWING EACH STROBING PULSE ADAPTED TO TERMINATE THE OUTPUT SIGNAL THEREOF, AND MEANS RESPONSIVE TO SAID REGENERATIVE FEEDBACK SIGNAL TO APPLY A FURTHER SIGNAL TO THE INPUT OF SAID AMPLIFYING MEANS FOR RENDERING INEFFECTIVE THE FIRST DISABLING PULSE FOLLOWING THE STROBING SIGNAL WHICH INITIATED SAID OUTPUT SIGNAL. 